The long term goal of this research is a better understanding of the processes which lead to bone resorption and accretion in vivo. At present much of the work deals with the role of bone blood flow in the regulation of skeletal metabolism. Specific aims include: (a) To study the mechanisms which regulate arteriovenous calcium and phosphate gradients acrose bone. (b) To investigate the role of bone blood flow in long term bone resorption and accretion. (c) To elucidate the mechanisms which regulate skeletal blood flow. (d) To study the role of calcitonin in calcium homeostasis. BIBLIOGRAPHIC REFERENCE: Boelkins, J. N., M. Mazurkiewicz, P. E. Mazur and W. J. Mueller. Changes in blood flow to bones during the hypocalcemic and hypercalcemic phases of the response to parathyroid hormone. Endocrinology 98: 403-412, 1976. Mueller, W. J. Egg shell formation and skeletal metabolism. In: P. E. Sturkie (ed.), Avian Physiology. Springer Verlag, New York, 1976, pp. 320-330.